Browsing by Author "Page RA"

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    A Narrative Review of Human Clinical Trials on the Impact of Phenolic-Rich Plant Extracts on Prediabetes and Its Subgroups
    (MDPI (Basel, Switzerland), 22/10/2021) Lim WXJ; Gammon CS; von Hurst P; Chepulis L; Page RA
    Phenolic-rich plant extracts have been demonstrated to improve glycemic control in individuals with prediabetes. However, there is increasing evidence that people with prediabetes are not a homogeneous group but exhibit different glycemic profiles leading to the existence of prediabetes subgroups. Prediabetes subgroups have been identified as: isolated impaired fasting glucose (IFG), isolated impaired glucose tolerance (IGT), and combined impaired fasting glucose and glucose intolerance (IFG/IGT). The present review investigates human clinical trials examining the hypoglycemic potential of phenolic-rich plant extracts in prediabetes and prediabetes subgroups. Artemisia princeps Pampanini, soy (Glycine max (L.) Merrill) leaf and Citrus junos Tanaka peel have been demonstrated to improve fasting glycemia and thus may be more useful for individuals with IFG with increasing hepatic insulin resistance. In contrast, white mulberry (Morus alba Linn.) leaf, persimmon (Diospyros kaki) leaf and Acacia. Mearnsii bark were shown to improve postprandial glycemia and hence may be preferably beneficial for individuals with IGT with increasing muscle insulin resistance. Elaeis guineensis leaf was observed to improve both fasting and postprandial glycemic measures depending on the dose. Current evidence remains scarce regarding the impact of the plant extracts on glycemic control in prediabetes subgroups and therefore warrants further study.
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    Hypoglycemic effects of antioxidant-rich plant extracts on postprandial glycemic responses in participants with prediabetes (GLARE study)
    (Food Science Publisher on behalf of the Academic Society for Functional Foods and Bioactive Compounds (ASFFBC), 15/11/2021) Lim WXJ; Gammon CS; Von Hurst PR; Chepulis L; Mugridge O; Page RA
    Background: Plant extracts may help to improve glycemic control in individuals with poor glycemic control. However, few studies have been investigated in the prediabetes cohort, which is a high-risk condition for T2DM. Thus, this study aimed to investigate the acute effect of grape seed, rooibos tea, and olive leaf extracts on postprandial blood glucose and insulin in participants with prediabetes. Methods: An acute, single-blind, placebo-controlled, non-randomized, crossover study (ACTRN12617000837325) where placebo and extracts of grape seed, rooibos tea and olive leaf standardized for total antioxidant capacity were given separately during an oral glucose tolerance test to participants (n=19, five men and fourteen women, aged 65.0 ± 1.6 years, Body Mass Index (BMI) 27.3 ± 1.1 kg/m2) with prediabetes (Glycated hemoglobin A1c (HbA1c) 42 ± 1 mmol/mol). The primary outcome incremental area under the curve of glucose (iAUCglucose) was examined with other glycemic measures. Data was analyzed using linear mixed model for repeated measures. Secondary analysis was conducted by stratifying participants into either a healthier or less healthy subgroup based on the postprandial time to glucose and insulin peaks, with the less healthy subgroup experiencing delayed glucose and/or insulin peaks. Results: There were no overall significant changes to glucose and insulin measures between all plant extracts and placebo (p>0.05). Upon secondary analysis, all extracts affected glycemic responses in the less healthy subgroup. Compared to placebo, grape seed reduced plasma iAUCglucose (p=0.016, 21.9% reduction), 2 h postprandial glucose (2hPG) (p=0.034, 14.7% reduction) and metabolic clearance rate of glucose (MCRglucose) (p=0.016, 16.7% increase). It also improved insulin indices such as 2 h postprandial insulin (2hPI) (p=0.029, 22.4% reduction) and Stumvoll overall insulin sensitivity index (ISIoverall) (p=0.028, 15.0% increase). Rooibos tea extract significantly improved β-cell function as demonstrated by the increased oral disposition index (DI) (p=0.031, 32.4% increase) compared to placebo. Olive leaf extract significantly increased incremental area under the curve of insulin (iAUCinsulin) (p=0.040, 16.7% increase). Conclusion: Grape seed, rooibos tea and olive leaf extracts demonstrated acute hypoglycemic benefits in adults with prediabetes and having less healthy metabolic profiles. A chronic study on the plant extracts is warranted to determine their longer-term impact on prediabetes. Trial Registration ID: ACTRN12617000837325
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    The Hypoglycaemic Effects of the New Zealand Pine Bark Extract on Sucrose Uptake and Glycaemic Responses in Healthy Adults—A Single-Blind, Randomised, Placebo-Controlled, Crossover Trial
    (MDPI (Basel, Switzerland), 2025-07-09) Lim WXJ; Page RA; Gammon CS; Moughan PJ; Novoa DMA; Silva FRMB
    Background: The New Zealand pine bark has been demonstrated in vitro to inhibit digestive enzymes involved in carbohydrate digestion (alpha-amylase, alpha-glucosidase, and dipeptidyl-peptidase 4 (DPP-4)). Objective: This study aims to investigate the inhibitory effects of the New Zealand pine bark on sucrose uptake and glycaemic responses in humans. Methods: A single-blind, randomised, placebo-controlled, crossover trial was carried out involving healthy adults (n = 40 (M: 12, F: 28), 30.1 ± 1.3 years, BMI 23.4 ± 0.5 kg/m2, HbA1c 32.5 ± 0.6 mmol/mol, FBG 4.7 ± 0.1 mmol/L). A control (75 g of sucrose powder only), and two doses of the pine bark extract (50 and 400 mg) were provided on separate occasions, with 75 g of sucrose mixed in 250 mL of water. Blood samples were collected at −10, 0, 15, 30, 45, 60, 90, and 120 min via a finger prick test. A linear mixed model for repeated measures (SPSS v30, IBM) was applied, and data presented as model-adjusted mean ± SEM. Results: Compared to control (247.5 ± 14.0 mmol/L⋅min), the iAUCglucose was significantly reduced with the 400 mg dose (211.8 ± 13.9 mmol/L⋅min, 14.4% reduction, and p = 0.037), but not with 50 mg dose (220.8 ± 14.2 mmol/L⋅min, 10.8% reduction, and p = 0.184). Compared to control (9.1 ± 0.2 mmol/L), glucose peak value was significantly reduced with the 50 mg dose (8.6 ± 0.2 mmol/L, 5.5% reduction, and p = 0.016) but not with the 400 mg dose (8.7 ± 0.2 mmol/L, 4.4% reduction, and p = 0.093). There were no statistically significant changes in postprandial insulin levels with the pine bark extract compared to control. Conclusions: The New Zealand pine bark extract attenuated sucrose uptake with improved glycaemic responses, and may therefore be useful as a hypoglycaemic adjunct to the diet.
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    The Inhibitory Effects of New Zealand Pine Bark (Enzogenol®) on α-Amylase, α-Glucosidase, and Dipeptidyl Peptidase-4 (DPP-4) Enzymes.
    (MDPI (Basel, Switzerland), 12/04/2022) Lim WXJ; Gammon CS; von Hurst P; Chepulis L; Page RA
    The New Zealand pine bark extract (Enzogenol®) has previously been shown to elicit acute hypoglycaemic effects in humans. The present study investigated the underlying mechanisms of Enzogenol® in reducing postprandial glucose in humans. The potential inhibitory action of Enzogenol® against digestive enzymes: α-amylase and α-glucosidase, and dipeptidyl peptidase-4 (DPP-4) enzyme was determined. Enzogenol® demonstrated the ability to inhibit all three enzymes: α-amylase enzyme activity (IC50 3.98 ± 0.11 mg/mL), α-glucosidase enzyme activity (IC50 13.02 ± 0.28 μg/mL), and DPP-4 enzyme activity (IC50 2.51 ± 0.04 mg/mL). The present findings indicate the potential for Enzogenol® to improve postprandial glycaemia by delaying carbohydrate digestion via the inhibition of digestive enzymes (α-amylase and α-glucosidase), and enhancing the incretin effect via inhibiting the dipeptidyl-peptidase-4 enzyme. The inhibitory actions of Enzogenol® on enzymes should therefore be further validated in humans for its potential use in type 2 diabetes mellitus prevention and management.
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    VEGF-A cis-located SNPs on human chromosome 6 associated with VEGF-A plasma levels and survival in a coronary disease cohort
    (BioMed Central Ltd, 2025-12) Meza-Alvarado JC; Pilbrow AP; Frampton CM; Cameron VA; Richards AM; Troughton RW; Doughty RN; Page RA; Mallard B; Bromhead C; Palmer BR
    Background: Cardiovascular disease (CVD) is the leading cause of death worldwide. Risk stratification of CVD patients may be improved by predictive biomarkers, including genetic markers. Elevated circulating vascular endothelial growth factor A (VEGF-A) levels have been linked to CVD development. We explored whether single nucleotide polymorphisms (SNPs) at the VEGFA locus on human chromosome 6 were associated with VEGF-A levels and clinical outcomes in established CVD. VEGF-A levels were compared between coronary heart disease patients and heart healthy controls. Methods: Imputed genotypes of 30 SNPs from the VEGFA region for 1935 patients from the Coronary Disease Cohort Study (CDCS) and 1183 individuals from the Canterbury Healthy Volunteers Study (HVOL) were analysed for associations with cardiometabolic parameters. Association with clinical endpoints was assessed using Kaplan-Meier analysis and multivariate regression models. To validate the findings from imputed data, DNA samples of 2027 CDCS patients and 227 HVOL participants were manually genotyped for variants rs6921438 and rs7767396. Baseline plasma VEGF-A assayed by ELISA in 227 HVOL participants was compared with levels in 549 CDCS patients. Results: Manual genotyping showed rs6921438 AA and rs7767396 GG genotype groups had lower VEGF-A levels at baseline (CDCS: rs6921438 AA (27.7 pg/mL), AG (43.3 pg/mL), GG (63.2 pg/mL), p = 4.49 × 10− 22; rs7767396: GG (27.4 pg/mL), AG (42.8 pg/mL), AA (61.5 pg/mL) p = 3.47 × 10− 21; HVOL rs6921438 AA (12.8 pg/mL), GA (19.9 pg/mL), GG (26.4 pg/mL) p = 0.021; rs7767396 GG (12.6 pg/mL), AG (19.6 pg/mL), AA (25.9 pg/mL) p = 0.029). In the CDCS cohort rs6921438 AA was associated with increased risk of all-cause death (p = 0.03); non ST-elevated myocardial infarction (NSTEMI, p = 0.0003), heart failure (HF, p = 0.035) and major adverse cardiovascular events (p = 0.032); rs7767396 GG was associated with increased NSTEMI (p = 0.001) and HF (p = 0.023) risk; rs6921438 AA (Hazard Ratio (HR) = 6.55 p = 0.017), rs7767396 GG (HR = 0.149, p = 0.017) and VEGF-A (HR = 2.55, p = 0.018) were independent HF admission risk predictors. Conclusions: Variants rs6921438 and rs7767396 are associated with plasma VEGF-A levels. Both SNPs and VEGF-A may be useful in prognosis for HF after acute coronary events.
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    VEGF-A related SNPs: a cardiovascular context.
    (2023) Meza-Alvarado JC; Page RA; Mallard B; Bromhead C; Palmer BR
    Cardiovascular diseases (CVDs) are the leading cause of death worldwide. Currently, cardiovascular disease risk algorithms play a role in primary prevention. However, this is complicated by a lack of powerfully predictive biomarkers that could be observed in individuals before the onset of overt symptoms. A key potential biomarker for heart disease is the vascular endothelial growth factor (VEGF-A), a molecule that plays a pivotal role in blood vessel formation. This molecule has a complex biological role in the cardiovascular system due to the processes it influences, and its production is impacted by various CVD risk factors. Research in different populations has shown single nucleotide polymorphisms (SNPs) may affect circulating VEGF-A plasma levels, with some variants associated with the development of CVDs, as well as CVD risk factors. This minireview aims to give an overview of the VEGF family, and of the SNPs reported to influence VEGF-A levels, cardiovascular disease, and other risk factors used in CVD risk assessments.